Water is one of the most
commonly used substances on our earth. We need water for all our
activities in day-to-day life. Water supply in urban area is always short
against the total demand. Surface water is inadequate to meet our demand
and we have to depend on ground water. Due to rapid urbanization,
infiltration of rainwater into the subsoil has decreased drastically and
recharging of ground water has diminished. This scenario requires an
alternative source to bridge the gap between demand and supply. Rainwater,
which is easily available and is the purest form of water, would be an
immediate source to augment the existing water supply by "catching water
wherever it falls".

Rainwater Harvesting has
emerged as a viable alternative to traditional perennial sources of water
in hilly areas, in places where the level of fluoride and arsenic is above
permissible limits and in urban areas facing water shortage and flooding
during monsoons.

Rainwater Harvesting (RWH)
is the process of collecting and storing rainwater in a scientific and
controlled manner for future use. Rainwater Harvesting in urban areas
include

Rainwater Harvesting in
large areas with open ponds, lakes, tanks etc.

Benefits of Rainwater
Harvesting

Environment friendly and
easy approach for water requirements

RWH is an ideal solution for water requirements in areas having
inadequate water resources

Increases ground water level

Improves ground water quality

Mitigates the effects of drought

Reduces the runoff, which other wise flood storm water drains

Reduces flooding of roads and low-lying areas

Reduces soil erosion

Cost effective and easy to maintain

Reduces water and
electricity bills

Rainwater Harvesting

Traditional Water
Harvesting in Karnataka underlines the importance of step wells, lakes,
tanks, channels etc., as water storage bodies, the basic purpose of
which was to establish a chain of water storage structures. However, a
vanishing "Lake Culture" due to urbanization and industrialization has
caused these systems to be neglected.

To make Rainwater
Harvesting (RWH) a success, we should have a thorough knowledge of the
following:
geographic location; climate; geology; soil; land use; water
requirements; existing water supply system; cost of water; systems &
forms of RWH and the potential of harvesting rainwater.

RWH has the following
unique advantages

Capturing rainwater
in-situ and augmenting supply water at a marginal cost

Replenishing groundwater
through recharging of rainwater by using the soil column

Reducing pollution and
contamination

Reducing the water bill
for the state exchequer

Providing clean and safe
water

Least capital investment
with maximum benefits to households and the city as a whole

The demerits of RWH

It is dependent on the
monsoons and intensity of rainfall.

It depends on intensive
participation from house level to the city level.

It is only a
supplementary source and cannot replace the existing supply system
completely.

Quality of rainwater harvested

As the primary source of water, rainwater is the purest form of water.
Rainwater harvesting not only solves the problem of availability of
water, but also provides good quality water.

However, certain precautions need to be taken to ensure that the
stored water is not polluted.

Keep the roof or the
water collection area clean before the rains.

Flush the rainwater
collected in the first few minutes.

Store the collected
rainwater in a closed container (avoid sunlight).

The quality of water
deteriorates in the presence of sunlight and air.

Water can be kept clean
over a period of five to six months in a clean container stored in an
enclosed area protected from sunlight.

Rainwater harvesting potential in urban areas is huge. Considering the
availability of rainwater in a residential site of 40 x 60 feet (an area
of 2400sq.ft./223 sq.mts.), around 2,23,000 lts of rainwater can be
harvested in a location where the rainfall is around 1000 mm or 39.4
inches (Bangalore receives around 1000 mm of rainfall annually). The
amount of rainwater that can be harvested from the available rainwater
in the plot depends on potential rainfall, catchment area available,
collection methods and its efficiency etc.

Rainwater Harvesting for Domestic Applications

Water requirement of a house can be broadly classified into

Drinking

Cooking

Bathing

Washing

Vehicles

Utensils

Clothes

Floor cleaning

Gardening

Flushing in toilets

For washing, gardening and flushing toilets, relatively less clean
water can be used (secondary use).

Rainwater Harvesting (RWH) can meet all these above needs with
suitable RWH techniques.

Water requirement in a house is throughout the year. However,
rainwater availability without having facilities to store is limited
to number of rainy days and the quantity of rainwater available during
the rainy days. Several interventions can be made to enhance the
number of days of use of rainwater from number of rainy days to 365
days a year. Parameters, which support rainwater harvesting, are
availability of space, willingness to invest, technical suitability of
soil structure and geological parameters.

The text and images used in this webpage are taken from the
book"Amruthavarshini - A guide for Rainwater Harvesting"
published by Karnataka State Council for Science and Technology.